Wave synthesizing network



PJW. KLIPSCH ETAL ,803

WAVE SYNTHESIZING NETWORK Filed Aug. 25. 1938 9 '-/O lit: 8

Feb. 4, 1941.

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WAVE smwnnsxzme umwoax Filed Aug. 25, 1938 2 Shests-Sheet 2 arvuc/Mou 5.8. WEST R W KLIPSCH IMG. MELARRY BILINSKY Patented Feb 4, 1941 y g 2,230,803

UNITED STATES PATENT OFFICE WAVE SYNTHESIZING NETWORK- Paul W. Klipsch, Samuel S. West, Solomon Bilinsky, and Weldon G. McLarry, Houston, Tex.

Application August 25, 1938, Serial No. 226,668 Claims. (01. 175-182) This invention relates to electrical filter cirfor wave form analysers by providing means for cuits and particularlythose circuits which proproducing wave forms ofpredetermined adjustduce predetermined amounts of transient disable characteristics. tortion. It also relates to the art of electrical These and other objects will be evident from 6 prospecting for buried deposits in the earths the following description taken in connection crust characterized by causing transient, interwith the drawings in which:

mittent, or periodic currents to flow in the earth, Fig. 1 is a block diagram of the apparatus used.

and noting, the wave form distortion in the po- Figs. 2, 3, and 4, are schematic diagrams of tential detected atadistance from the region suitable distorting networks. where current is caused to flow. Fig. 5A is a convenient distorting network and 10 In a copending application Serial No. 103,129 Fig. 5B shows the response of the parts and of for Method ofsub-surfac'e prospecting there has the whole network to a unit impulse.

been disclosed a method of geophysical explora- Fig. 6 is the equivalent in performance of Fig.

tion which depends upon observing the wave 5A, differing therefrom in that both input and form distortion which results when an alternatoutput circuits may be grounded. 1 5

ing current is caused to flow in the earth and Figs. 7A and 7B show circuits which have simithe detected potentialwave form is compared lar responses and are therefore potentially with the generatedwave form. In an embodiequivalent. ment of that invention, alternating current, or Fig. 1 shows the general plan of an exploraa simple transient current as proposed by Blau tion method in which an electric generator I of 20 in Patent No. 1,911,137, is caused to flow between suitable wave form causes current to flow in the two electrodes embedded in the earths crust, earth 2 between electrodes 3 and 4. Spaced from and the resultant potential between two other the region of generation, detector electrodes -5 electrodes is detected and its wave form comand 6 pick up a potential which is amplified pared to that of the, current or the potential in repeater I and the wave form ofthe potential 5 causing it, exhibited on indicator 8 which may be a cathode As a means of comparison, a wave similar to ray or other oscillograph the generated wave is distorted in a network, In order to measure the distortion produced ,superimposed on the detected wave in phase opin the wave form a null method is used. A 3 position, and the amplitude and distortion varied second generator 9 generates a potential subuntil it compensates the detected wave, an oscilstantially similar in wave form to the current lograph or oscilloscope giving a null indication Wave of generator I. This potential which is of when this compensation is complete. Then the variable amplitude and which is substantially constantsof the distorting network serve directly in synchronism with the current wave of the 5 or indirectly as a measure of the wave distortion. generator I is introduced into a wave distortion The various amounts'and types of distortion are network I0 in which the wave shape may be sethen indicative of the formations traversed by lectively modified until it closely approximates the current in the earth. the incoming wave. By adopting the correct An object of the present invention is to propolarity and adjusting the amplitude of the po- 4 vide distorting networks for geophysical prostential from the generator 9'the modified potenpecting by the above method such that wave tial is caused to oppose the detected wave, and forms produced by currents flowing in the earth when the two wave shapes are similar the indican be duplicated in apparatus having known cator shows a null. characteristics. In a form of the invention to be explained, Another object is to provide circuits through generators I and 9 produce currents whose wave 45 which transient electric waves, or intermittent form is rectangular, so that they may be reprewaves of predetermined wavefronts are transsented by Heaviside's unit function (see for exmitted with predetermined amounts of waveampie chapters IV and V, Operational'Circuit form distortion. Analysis by V. Bush, John Wiley & Sons, 1929). It is also an object to provide circuits whose obviouslm the trans ent thus produced y e 50 performance in transmitting electric impulses repeated intermittently or periodically.

can be varied such that the resultant wave form The distorting network 10 inaccorda-nce with is similar to that observed in passing electric the invention may take on various forms as will waves through the earths crust. be made more fully apparent; i

Another object is to provide calibrating means In Fig. 2 there is shown a half-section which 55 may be adjusted to different amounts of transient distortion.

Fig. 3 shows a bridged T suitable for the purpose of this invention. This circuit has the ad- 5 vantage that it constitutes a network of constant impedance so that its insertion would not affect other apparatus such as generators, amplifiers, or attenuators to which it is attached.

Fig. 4 shows a circuit in which two exponentials may be produced. That is, with a unit tunction input, the output voltage will be where A0, A1 and A2 are adjusted by potential dividers R11 and R12, and time constants a1 and (12 are adjusted by varying C13 and C2: or R1; and R22. proximation, it is necessary that R14 R12 R11 (2) Rz4 R22 R21 --(3) Obviously Equation 1 may bemade to contain more terms by simply adding potentiometers and associated circuit elements which might be denoted R31, R32, D33 etc.

Equation 1 may be said to define the indicial response of the circuit of Fig. 4. If Equation 1 expressed current in some branch of the circuit, it would define the transfer indicial admittance (see for example Bush, loc. cit. chap. IV.). 7

Fig. 5A shows another circuit and Fig. 5B showstypical indicial responses pertinent to each part of the circuit and the whole. Thus in Fig. 5B, a shows the potential produced across: C1, 1) shows the potential across the lower part of R11, shows the potential across R2, and d shows the whole potential across the output terminals 53, 54.

The circuit of Fig. 6 is equivalent to that of 40 Fig. and has the advantage of being a 3-terminal network whose common terminal maybe grounded for stability and to avoid otherwise uncontrollable capacitances to ground. The transformer T must have a leakage inductance whose 5 reactance is small compared to the load across it at the highest frequencies to be transmitted. Also, the transformer T should have a shunt inductance which is sufficiently large, as compared with the impedances between which it is con- 50 nected, so that its time-constant is long compared to the time constant of R 02. In this manner the requirements of this element ofthe network are readily met.

Figs. 7A and 7B illustrate the principle of equivalents. These two circuits are exactly equivalent if fi=R2c. 60 R2 R11 --(5) R3 R11 --(6) In the practice of the invention the wave shape of thedetected wave is caused to be nullified by 65 the wave produced by the synthesizing circuit For an understanding of the operation of the invention, it has been explained on the assump- 7 tion that the generators land 9 producestep- In order that Equation 1 be; a close ap like or unit function impulses. This is not necessary however; any wave form possessing frequency components (harmonics) over a sufficient range, say from 50 to 1000 cycles is suitable, provided that the wave forms of both generators are substantially similar. Regardless of the particular wave form used, when a balance or null is obtained the indicial response of the earth must be closely approximated by the indicial response of the network.

For simplicity in nomenclature a reactanceresistance combination such as R12, C13 in Fig. 4, R1, C1 in Fig. 6 or L2, R3 in Fig. 7B will be referred to as a time-constant circuit, the principal property of which is the time constant which is numerically determined by the R-C product or The invention claimed is:

1. Apparatus for electrical prospecting comprising means for causing current impulses to flow in the earth, means for indicating the wave form of a potential derived from said current, means for generating another wave form for the purpose of comparison with said potential wave form comprising an impulse generator, means for dividing the potential output of said generator into at least two portions, means for applying each of at least two of said portions to two different time-constant circuits of the reactanceresistance type, and means for taking ofi'a voltage across the resistance of one' of said timeconstant circuits and a voltage across the reactance of another of said time-constant circuits, and combining them to form an outputvoltage for comparison purposes.

2. Apparatus iorelectrical prospecting comprising means forcausing current impulses to flow in the earth. means for indicating the wave form of a, potential derived from said current,

means for generating another wave form produced for purposes of comparison with said potential wave 'form comprising an impulse generator and an electrical network between said generator and said indicating means including a plurality ofv time-constant circuits of the resistance-reactance type, means for applying at least part of the voltage output to said generatoracross each of saidtime-constant circuits, means for taking off a voltage across a reactance of one of said time-constant circuits, means for taking off a voltage across a resistance of at least another of said time-constant circuits, means for passing at least part of the voltage output of said generator through said network unaltered, and means for combining this unaltered voltage with the aforesaid voltages taken off the timeconstant circuits and applying the combination to the indicating means.

3. Apparatus for electrical prospecting comprising means for causing current impulses to flow in the earth, means for indicating the wave form of a potential derived from said constant, means for generating another wave form for purposes of comparison with said potential wave form including a generator of a wave form suitable for comparison with said potential wave form after suitable modification, a resistance arranged across the output of said generator, at least two different time-constant circuits connected across different portions of said resistance, the total impedance of each of said time-constant circuits being aslarge compared to the value of the portion with the resistances across which it is connected, means for taking ofi a voltage across a reactance of one of said time-constant circuits, means for taking off a voltage across a resistance of another of said time-constant circuits, and means for combining these voltages and applying them to the indicating means.

4. An apparatus according to the preceding claim in which the time-constant circuits are so connected to the resistance that the steady state value of the voltage fed from said network to the indicator will always be the same regardless of the size of the portion of the resistance which is included in the respective time-constant circuits.

5. A circuit for generating a wave form of predetermined shape comprising a. generator of a SAMUEL S. WEST. PAUL W. KLIPSCH. WELDON G. MCLARRY. SOLOMON BILINSKY. 

